FIG. 11 shows a portion of the prior art semiconductor laser device described in "Examination Of An Optical Transmission/Receive Module According To Microoptics Part Mounting Technique Employing A Silicon Substrate" by Miyagawa et al, Proceedings of the 1992 IEICE Spring Conference, Part 4 C-271. This prior art example incorporates a semiconductor laser with an optical element, such as a lens, for efficiently introducing light output from a semiconductor laser device into an optical fiber.
In FIG. 11, a semiconductor laser chip 2, a monitor photodiode 3, and a spherical lens 4 are mounted on a silicon substrate 1 and the spherical lens 4 is put in a positioning hole 5 so that it is located at a predetermined position relative to the semiconductor laser chip 2. Electrodes 6a and 6b are bonding pads and a bonding wire 7 connects an upper electrode 2a of the semiconductor laser chip 2 and the electrode 6b.
The semiconductor laser chip 2 is welded to a die pad (not shown) on the silicon substrate 1 for position determination. The die pad is connected to an electrode 6a and has approximately the same size as the bottom surface of the semiconductor laser chip 2, and the lower electrode of the semiconductor chip 2 is electrically connected to the electrode 6a via the die pad.
The positions and configurations of the electrodes 6a and 6b, the die pad, and the positioning hole 5 can be established with high precision employing the photolithography techniques used in the manufacture of a silicon integrated circuit.
The size of the spherical lens 4 and the size and depth of the positioning hole 5 are controlled in their production so that the spherical lens 4 occupies a desired position relative to the light emitting point of the semiconductor laser chip 2, i.e., so that the light emitting point of the semiconductor laser chip 2 and the focal point of the lens 4 are aligned with each other. The spherical lens 4 is put in the positioning hole 5 and located at a particular position relative to the semiconductor laser chip 2, and the bottom of the spherical lens 4 is adhered to the silicon substrate 1 with a polyimide adhesive. In addition, a monitor photodiode 3 is arranged at a position opposite to the spherical lens 4 to monitor the light emitted from the rear of the semiconductor laser chip 2.
A silicon substrate 1 is formed with the dimensions required for the manufacture of a semiconductor laser device, for example, a length in the optical axis direction of 2.0-3.0 mm and a thickness of 1.0 mm.
Then, an InP series semiconductor laser chip 2, an InP-based monitor photodiode 3 having dimensions in both vertical and transverse directions of 500 .mu.m and a glass spherical lens of 300 .mu.m-1.0 mm diameter are produced in accordance with the dimensions of the semiconductor laser device.
Thereafter, as shown in the figure, the silicon substrate 1 is etched using photolithography techniques to produce a positioning hole 5 for mounting the spherical lens so that the light emitting point of the semiconductor laser chip 2 is located at the focal point of the spherical lens 4. The laser light from the light emitting point is then efficiently incident on the spherical lens 4.
By employing CrAu evaporation and photolithography techniques, a die pad comprising a CrAu film having the same configuration as the bottom surface of the semiconductor laser chip 2 is formed at a position where the semiconductor laser chip 2 is to be disposed, CrAu films are formed at positions where electrodes 6a and 6b are to be disposed on the silicon substrate 1, and, thereafter, Au electrodes 6a and 6b are formed on the CrAu films. In addition, the semiconductor laser chip 2 is adhered to the die pad by soldering employing AuSn or the like. Then, the lower electrode of the semiconductor laser chip 2 is connected to the electrode 6a via a die pad.
Then, a monitor photodiode 3 is fixed to an end of the silicon substrate 1 opposite the positioning hole 5 for the spherical lens 4 relative to the semiconductor laser chip 2 by soldering employing AuSn or the like so that the laser light emitted from the light emitting point of the semiconductor laser chip 2 and directed backward is monitored.
Next, an Au bonding wire connecting the upper electrode 2a of the semiconductor laser chip 2 to the electrode 6b is attached.
Then, the spherical lens 4 is put in the positioning hole 5, and the lower part of the spherical lens 4 and the bottom of the positioning hole 5 are adhered to each other with a small amount of polyimide-based adhesive, thereby completing the prior art semiconductor laser device.
In this way, the semiconductor chip 2, the monitor photodiode 3, and the spherical lens 4 are placed on a silicon substrate 1, thereby producing a semiconductor laser device than can easily introduce light into an optical fiber. In this construction, however, it is required to place each of the constituent parts, i.e., the semiconductor laser chip 2, the monitor photodiode 3, and the spherical lens 4, at predetermined positions, resulting in complicated work.
FIG. 18 shows a structure for another prior art semiconductor laser device. In the figure, reference numeral 1 designates an Si supporting substrate, reference numeral 4 designates a spherical lens, reference numeral 5a designates a V-shaped groove for positioning produced by etching, and reference numeral 2 designates a semiconductor laser chip.
Anisotropic etching of the Si supporting substrate is carried out with KOH whereby a V-shaped groove having a predetermined aperture width and a predetermined depth is produced. Then, the semiconductor laser chip is positioned relative to the position of the lens 4 by soldering. Further, the spherical lens 4 is engaged in the V-shaped groove 5a and is fixed in place with a resin or the like whereby a semiconductor laser device is produced.
In this semiconductor laser device, lens position is determined by placing the spherical lens 4 in contact with the V-shaped groove 5a and, therefore, the depth and width of the V-shaped groove 5a determine the coupling efficiency between the laser chip 2 and the spherical lens 4. The method of producing the V-shaped groove 5a by combining masking and wet etching is an industrial method that is superior but, when the laser devices are mass-produced, the aperture width of the mask can vary or the width and depth of the V-shaped groove are difficult to reproduce, reducing the coupling efficiency between the laser chip 2 and the lens 4, resulting in reduction in production yield.
In addition, in the prior art semiconductor laser device, the position of the spherical lens is determined by fixing the spherical lens in a positioning aperture. However, variations arise in the width and depth of the positioning aperture due to errors in controlling the etching, so that it is impossible to fix the spherical lens in a predetermined position whereby there is a reduction in production yield.